Due to emission of greenhouse gas caused by the use of fossil fuels, global warming has resulted in changes in climate and global environment, thereby threatening the survival of all living things on earth including human beings. Accordingly, various researches and developments for reducing carbon dioxide are now in progress. As one of efforts, study on the way of capturing and biologically converting carbon dioxide is actively underway.
As a green plant which performs photosynthesis for biologically converting carbon dioxide, microalgae have been actively studied. In common with other green plants in photosynthetic process, microalgae, phytoplankton, use sun as an energy source and grow up with photosynthesis for biofixation of carbon dioxide.
The first reason for recognizing microalgae as a means of biofixation of carbon dioxide is very low amount of energy to be injected for capturing carbon dioxide, because solar energy may be the main energy source as the same with absorption of carbon dioxide. Thus, since there is less amount of generating carbon dioxide for operation of biofixation of carbon dioxide, removal efficiency is high in terms of profit balance of carbon dioxide.
Secondly, required size of site is small because of very high speed of fixation of carbon dioxide as compared to green plants. According to results from study conducted at Tokyo Electric Power Research Institute, it is revealed that the speed of fixation of carbon dioxide of microalgae is more than 8 times higher than that of macroalgae and more than 16 times higher than that of pine trees, the most common tree in Korea.
Besides, there is an advantage in that processes for separating and concentrating carbon dioxide are not required due to direct fixation of carbon dioxide from combustion gas. Moreover, microalgae, generated from carbon dioxide fixation, contain numerous useful materials, thereby being utilized for manufacture of expensive bioproducts.
However, if the carbon dioxide fixation process using microalgae is conducted by bioreactors applied to industries, it takes too much electric energy. Thus, it is not easy to supply light energy which is necessarily required for energy saving and microalgae growth.
To solve a problem, Korean Patent Registration no. 10-1072844 (DEVICE FOR CULTIVATING MICROALGAE BY USING EMITTED GAS FROM POWER PLANT) was filed and published.
As illustrated in FIG. 1, the device for cultivating microalgae by using emitted gas from power plant includes a cultivation area (10), an exhaust gas supply area (20) and a microalgae extraction area (30).
The cultivation area (10) consists of a photosynthesis reactor (11) for cultivating microalgae, which is microbial, and a light emitting member (13) for shining light on the photosynthesis reactor (11). Installed to the inside of a greenhouse for maintaining optimal temperature, the cultivation area (10) is provided with exhaust gas from a power plant (1) through the exhaust gas supply area (20).
Specifically, the photosynthesis reactor (11) has a plurality of exhaust gas supply lines (15) for effectively supplying exhaust gas, coming from the exhaust gas supply area (20), and a shut-off valve (15a) in each exhaust gas supply line (15). Also, the photosynthesis reactor (11) has a drain line (17) for emitting microalgae, which stays inside, and a water supply line (19) for adding water toward the inside.
The photosynthesis reactor (11) not only balances cultivation environment of microalgae by means of carbon dioxide (CO2) and heat in exhaust gas, but increases the amount of cultivated microalgae.
The light emitting member (13) is used for stimulating cultivation of microalgae at night or a cloudy day.
The exhaust gas supply area (20) connects the power plant (1) and the cultivation area (10) for supplying exhaust gas, generated from the power plant (1), to the cultivation area (10).
The exhaust gas supply area (20) consists of a vent fan (21), a filter member (23) and a heat exchanging area (25).
Connected to a vent line (3) of the power plant (1), the vent fan (21) compulsorily draws in part of exhaust gas emitted to a stack (5) throughout the vent line (3) and then, delivers to the photosynthesis reactor (11).
The filter member (23) eliminates foreign substances contained in exhaust gas which is discharged by the vent fan (21).
The heat exchanging area (25) performs heat exchange of exhaust gas to reduce temperature of exhaust gas which passes through the filter member (23).
Property reduced temperature in the heat exchanging area (25), exhaust gas is supplied to the photosynthesis reactor (11) throughout a supply line (15), thereby making carbon dioxide eliminated.
The microalgae extraction area (30) is comprised of a drainage pump (31), installed in the drain line (17) of the photosynthesis reactor (11); a storage tank (33) for storing water discharged from the drain line (17); and a separation member (35) for separating water and microalgae.
The drainage pump (31) compulsorily discharges microalgae, cultivated in the photosynthesis reactor (11), to the storage tank (33). When microalgae is compulsorily discharged by the drainage pump (31), water in the photosynthesis reactor (11) is discharged together.
The storage tank (33) is connected to the separation member (35), and water, contained inside, is supplied to the separation member (35).
The separation member (35) consists of a centrifuge (35a) for separating water and microalgae by means of turning force and water of the storage tank (35); and a storage tank (35b) for storing water, discharged from the centrifuge (35a).
There are a plurality of centrifuges (35a) for optimizing efficiency in microalgae separation, and water, coming from microalgae separation, is discharged to the storage tank (35b). Although two centrifuges (35a) are illustrated in the present embodiment, the number of centrifuges (35a) may be one or more than three in accordance with a need of a user.
Discharged to the storage tank (35b) and fed to the heat exchanging area (25) by means of a drain water supply area (40), water is used as a medium of heat exchange of the heat exchanging area (25).
The drain water supply area (40) comprises a connection line (41) for connecting the storage tank (35b) and the heat exchanging area (25) in order to transfer water of the storage tank (35b) to the heat exchanging area (25); and a feed pump (43) installed on the connection line (41).
However, the traditional device for cultivating microalgae by using emitted gas from power plant includes the vent fan in the vent line. Thus, emitted gas is not actively supplied by differential gas pressure, and the photosynthesis reactor of the cultivation area is damaged by pressure or water is overflowed because of pulsatory supply.
In addition, in the traditional device for cultivating microalgae by using emitted gas from power plant, moisture in emitted gas makes the vent line full of water. Thus, it causes breakdown of the vent fan and gives a bad influence on microalgae growth due to water inflow into a photosynthesis cultivator.